1. Field of the Invention
The present application relates generally to methods for forming thin films comprising Group VA elements (Sb, As, Bi, P, N) by atomic layer deposition. Such films may find use, for example, in phase change memory (PCM) devices and in optical storage media.
2. Description of the Related Art
Thin films comprising group VA elements are used in many different applications, including, for example, non-volatile phase-change memories (PCM), solar cells, III-V compounds and optical storage materials. III-V compound semiconductors can be used in many different application areas, including transistors, optoelectronics and other application areas, for example, in bipolar transistors, field effect transistors, lasers, IR detectors, LEDs, wide band gap semiconductors, quantum well or quantum dot structures, solar cells and in monolithic microwave integrated circuits. The operation of PCM cells is based on the resistivity difference between amorphous and crystalline states of the active material. A resistivity difference of more than three orders of magnitude can be obtained by many different phase change alloys. The switching in a PCM cell is generally accomplished by heating the material locally with suitable current pulses, which, depending on the intensity of the pulse, leave the material in a crystalline or amorphous state.
A wide variety of different PCM cell structures have been reported, many of which use trench or pore-like structures. Sputtering has typically been used in preparing PCM materials, but the more demanding cell structures will require better conformality and more control of the deposition process. Sputtering may be capable of forming simple pore and trench structures, however, future PCM applications will require more complicated 3-D cell structures that cannot be formed using sputtering techniques. Processes with greater precision and control, such as atomic layer deposition (ALD), will be required to make these complicated structures. Using an atomic layer deposition process provides greater precision and control over the deposition, including better conformality and better control of the composition of the deposited film.
Atomic layer deposition processes for depositing Sb-containing thin films have been limited, in part, by a lack of appropriate precursors.
A need exists, therefore, for methods for controllably and reliably forming thin films of phase change materials comprising antimony by ALD from gas phase reactants.